The present invention relates to devices for converting free-space electromagnetic radiation to electrical power and in particular to a rectification element employing an electron shuttle useful for such a device.
“Rectennas” are antennas that may receive radio signals and rectify them to generate electrical power for wireless power transfer. An example rectenna system was used in 1964 to power a tethered helicopter holding the rectenna and receiving a beam of microwave radiation from a ground-based microwave transmitter.
Potential applications for rectennas include both large-scale power transfer applications such as the communication of power between satellite and earth based stations as well as smaller scale applications such as powering RFID tags, biomedical implants, or the like. The use of rectennas is not limited to radio signals but has been proposed for electromagnetic signals at light frequencies as an alternative to standard photocells.
A limitation in the use of rectennas, particularly for low power density radiation, comes from the rectifying element necessary to convert an electromagnetic signal to useful power. A free-space electromagnetic signal will, in general, be an alternating current (AC) signal with an average current (and voltage) of zero (zero bias). In order to obtain useful continuous electrical power, the AC signal normally must be converted by rectification to a signal with a non-zero average (DC signal).
Standard junction semiconductors, such as pn diodes, may be used for rectification but are relatively inefficient and have high forward bias voltages resulting in lost power in the junction during the rectification process. Such high forward bias values can also make it impractical to extract power from low power density signals where these voltages are not readily obtained at the antenna output. For light frequency electromagnetic signals, the junction capacitance of a standard junction diode can prevent the required high-speed operation.